The present application relates to a display device displaying images by using a light emitting element disposed for each pixel, and a method of driving the display device. Furthermore, the application relates to an electronic device having the display device.
Recently, in a field of display devices for image display, a display device using a current-drive optical element as a light emitting element of a pixel, the optical element being changed in luminance in accordance with a value of electric current flowing into the optical element, for example, a display device using organic EL (Electro Luminescence) elements has been developed and is being commercialized. The organic EL element is a self-luminous element unlike a liquid crystal element or the like. Therefore, the display device using organic EL elements (organic EL display device) does not need a light source (backlight), and therefore is high in image visibility, low in power consumption, and high in response speed of an element compared with a liquid crystal display that needs a light source.
A drive method of the organic EL display device includes simple (passive) matrix drive and active matrix drive as in the liquid crystal display. The simple matrix drive may simplify a device structure, but hardly increases display size and resolution. Therefore, the active matrix drive is being actively developed at present. In the active matrix drive, electric current flowing into a light emitting element disposed for each pixel is controlled by a driver transistor.
Generally, threshold voltage Vth or mobility v, of a driver transistor may be temporally varied, or may be different for each of pixels due to variation in a manufacturing process. When the threshold voltage Vth or the mobility v, is different for each pixel, a value of current flowing into the driver transistor varies for each pixel, and therefore even if the same voltage is applied to gates of driver transistors, luminance of an organic EL element varies for each pixel, leading to reduction in uniformity of a screen. Thus, a display device has been developed, which includes a function of correcting variation in threshold voltage Vth or mobility μ, (for example, see Japanese Unexamined Patent Application Publication No. 2008-083272).
In the active-matrix display device, any of a signal line driver circuit, which drives signal lines, a write line driver circuit, which sequentially selects a pixel, and a power line driver circuit, which supplies power to each pixel, is basically configured of a shift register (not shown), and has a signal output section (not shown) for each stage in correspondence to each pixel column or each pixel row. Therefore, when the number of pixel columns and the number of pixel rows are increased, the number of signal lines and the number of gate lines are accordingly increased, and the number of output stages of a shift register is correspondingly increased, leading to increase in size of a peripheral circuit of a display device.
Thus, a measure of sharing an output stage of a shift register has been taken in the past in order to reduce size of a peripheral circuit. For example, Japanese Unexamined Patent Application Publication No. 2006-251322 proposes a method where a signal line is shared by a plurality of pixels. According to this, each output stage of a shift register in the signal line driver circuit may be shared by a plurality of pixel columns, and a circuit scale, circuit area, and circuit cost may be correspondingly reduced